A Cold-Resistant Aerobic Denitrifying Bacterium Rhizobium pusense N7 for Aquaculture Wastewater Treatment and Its Denitrifying Characteristics

Aerobic denitrifying bacteria can effectively cope with the challenge of dissolving nitrogen in wastewater. High-performance aerobic denitrifying bacteria were isolated using the plate streaking method and subsequently evaluated and identified based on nitrate removal efficiency, nitrite accumulation, growth characteristics, morphological analysis, and 16S rRNA sequencing. Results showed that strain N7 achieved a nitrate removal rate of 92.53% at 15 °C, with a maximum removal rate of 28.15 mg·L−1·h−1. Molecular identification confirmed this strain as Rhizobium pusense N7. Optimization experiments established the ideal conditions for Rhizobium pusense N7: sodium succinate as the carbon source, C/N ratio of 15:1, temperature at 30 °C, shaking speed at 100 rpm·min−1, and initial pH of 7.0. During the application process, Rhizobium pusense N7 demonstrated efficient nitrogen removal, eliminating 18.3% of nitrate, 71.5% of ammonia nitrogen, and 26.9% of total nitrogen (TN) from aquaculture wastewater within 24 h. This study offers a promising solution for the biological treatment of wastewater under low-temperature conditions.